For realization with Google:
1. I registered ouath access to Testlink in:https://console.developers.google.com/apis/credentials [^] and got Client ID and Client secret key. Also I set url to Testlink
2. After I set these values in config file of Testlink.
3. During logon Testlink asks Google with these keys and gets form of login from Google.
4. After filling form Testlink receives successful token, check user-email in white list and perform creation of session
5. If user is not in Testlink db it is created with guest role and oauth authorization type

If readme.md I provided description of config variables and short description